Suburbanite

One of the much pointed out weak points of a much maligned oil filter is its 'cheap' (poorly functioning?) anti-drainback valve. Just wondering why it's so critical in an oil filter mounted vertically? Don't think there's enuf residual pressure after shutdown to force the oil out of the filter (but what do I know), so why would a poorly functioning or even non-functioning anti-drainback valve present a problem at startup?

RamDan03

I wouldn't think it is that big of a deal either. Since the filter is holding the oil like a bucket, there really shouldn't be any issues. I wouldn't think there would be enough backpressure in the system to do any harm. Also, you would have to park on a very steep incline to tilt the filter enough for it to empty out.

One of the only vehicles where I could see this anti-drainback valve being beneficial is the Mazda RX-7. The oil filter mounts on the top of the engine block upside down. If the valve failed, there would be no initial oil on startup. This is why I never used FRAM filters in the Mazda RX-7's I used to own. They had a weak valve and the filter would not hold the oil consistantly. However, Purolator seems to make an excellent filter for the money. If I couldn't get a Fleetgaurd for my Cummins, I wouldn't think twice about a Purolator.

Suburbanite

I admittedly don't understand oil flow very well but further thinking (oh no!) has got me suspecting that ANY oil remaining in the oil filter after shutdown isn't available to the engine at startup with or without an anti-drainback valve. I'm thinking that until oil pressure comes up ANY oil retained in the oil filter isn't available to the engine.

wannadiesel

[quote author=Suburbanite link=board=8;threadid=21988;start=0#msg205567 date=1067979743]
I admittedly don't understand oil flow very well but further thinking (oh no!) has got me suspecting that ANY oil remaining in the oil filter after shutdown isn't available to the engine at startup with or without an anti-drainback valve. I'm thinking that until oil pressure comes up ANY oil retained in the oil filter isn't available to the engine.
[/quote]
Yes, but if the filter is full of oil the pressure will come up sooner since the pump does not have to fill the filter. An ADV will keep the oil passages above it from leaking their contents back to the pan, so it is useful even on a "properly" oriented filter.